Check the gate clearance and use a purging compound grade that clears the tightest restriction. For instance, a glass-filled CPC is not recommended for purging most hot runner systems due to gate clearance restrictions and the potential to damage nozzle tips, as well as the possibility of fiber agglomeration at the gate.
Also, an effective CPC will remove carbonized resin and colorants, which may break off and block gates if their clearances are too small. Before purging hot runners, purge the screw and barrel to ensure that any contamination in the barrel doesn’t get into the hot runners.
Use a purging compound grade that is compatible with the processing resin being molded. This ensures less residue is left behind.
Typically, an open-mold or closed-mold method of purging can be used for hot runner cleaning. An open-mold method is best for cleaning lower cavitation manifolds, and higher cavitation molds are better cleaned via closed-mold purging.
For extremely difficult hot runner purges, try a chemical purging compound. The expansion into dead areas helps speed up the purging process and often prevents the need to send the hot runner back to the manufacturer for cleaning.
A high-quality CPC should leave low residue to make for quick and efficient purging. Purging compound suppliers recommend different procedures for purging hot runners, and the method chosen depends largely on the resin(s) being processed, mold design and cleaning difficulty. If you have any questions, be sure to consult your supplier.
Learn how to reduce machine downtime with five quick purging compound tips for your injection molding application.